1. Field of the Invention
This invention relates generally to a method for removing the ash mineral matter content of coal and more particularly to removing ash from coal and transporting the ash free coal in a slurry form.
2. Background of the Invention
The energy crisis has made inevitable an increasing use of coal as fuel for the generation of electicity, and has also been employed as the feedstock in processes for the conversion to gaseous and liquid hydrocarbonaceous products from which fuel gas, gasoline, residual fuel oil, and the like can be obtained. However, coal contains undesirable amounts of mineral matter (non-carbonaceous matter) and its removal improves the quality of the coal and makes it easier for specifications to be met, and renders the conditions of subsequent use of the coal more flexible.
Coal is generally classified in four groups: (1) anthracite, (2) bituminous, (3) sub-bituminous, and (4) lignite. The ash mineral matter content of these coals may vary from about 1 percent to as high as 50 percent by weight.
U.S. Pat. No. 3,998,604 to Hinkley, discloses a method for the demineralization of a low rank coal comprising the steps of forming the coal into a slurry, grinding the slurry in the presence of an aqueous acid such as HCl, H.sub.2 SO.sub.4, and H.sub.2 CO.sub.3 and the slurry is subjected to froth flotation in the presence of a gas selected from Cl.sub.2, SO.sub.2, or CO.sub.2.
It is known to transport coal by pumping it as a water or liquid carbon dioxide slurry through pipelines from a coal source point to a coal use point. U.S. Pat. No. 4,206,610 to Santhanam, discloses a method for transporting coal in finely divided form in a liquid carbon dioxide slurry wherein the liquid carbon dioxide used as the slurry liquid is formed by burning coal at the coal source point and liquifying the resulting gaseous carbon dioxide.
This is an improved method for removing the ash mineral content of coal utilizing liquid carbon dioxide combined with transporting ash free coal by pumping it as an ash free coal/liquid carbon dioxide slurry from the point of ash removal to a coal use point, recovering the liquid carbon dioxide slurry liquid at the coal use point and returning it for use in the ash removal step.